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Jan. 26, 2012 -- Boys tend to talk later than girls; they also acquire language skills at a slower rate than girls do. Now new research may point to why.

In a newly published study, umbilical cord blood was collected from nearly 900 Australian newborns and tested for testosterone. Newborn boys are exposed to 10 times the levels of testosterone before birth, compared to girls. Sex hormones, like testosterone, are known to play a key role in shaping how the brain develops.

“Language delay happens in about 12% of children, the majority of these being boys. For years, the possible causes have been a mystery,” says researcher Andrew J. O. Whitehouse, PhD, associate professor at the Telethon Institute for Child Health Research at the University of Western Australia in Perth.

“What we found was that exposure to increased levels of testosterone, particularly in males, may be one of the reasons for language delay,” Whitehouse tells WebMD. “Really it is the first sort of biological finding, sort of a biological risk factor, for language delay.”

Testosterone’s Effects

The study followed the children during the first three years of life, checking development stages each year.

They found that 3-year-old boys with the highest umbilical testosterone levels were more than twice as likely to screen positive for a language delay, compared to boys with the lowest testosterone levels.

The opposite was true for girls. In girls, higher testosterone was linked to a lower risk of language delay.

Researchers are still scratching their heads over why testosterone might have different effects on language in boys and girls. They say more studies are needed to answer that question.

Experts say the study only shows that higher measured testosterone during the newborn period may be associated with a language delay and not that it caused the delay in speech development.

“Really the biggest thing is that this may help us identify what are the actual neurological causes of a language delay, but it may also help us increase monitoring of children at risk,” Whitehouse says.

“If we identify kids exposed to higher levels of testosterone, maybe we can promote their language development from the very earliest stages of life,” he says.

Advice to Parents of Late Talkers

“We have certain developmental expectations for boys and girls,” says Diane R. Paul, PhD. Paul is director of clinical issues in speech-language pathology for the American Speech-Language-Hearing Association in Rockville, Md.

Paul says those developmental milestones are conservative and already account for sex differences.

She says parents should be concerned if children don’t meet those goals. “The earlier someone gets help, the better,” Paul says. “Early intervention is really a key to preventing later problems with reading, writing, and behavior.”

The study is published in the Journal of Child Psychology and Psychiatry.